1. Field of the Invention
The present invention relates to a Wireless Local Area Network (WLAN) mesh communication system. More particularly, the present invention relates to a scheduling method for transmitting and receiving a beacon message in a WLAN mesh communication system.
2. Description of the Related Art
In the next generation communication system, research for providing users with high speed services of various levels of Quality of Service (QoS) has been actively conducted. Specifically, research into a WLAN communication system has been performed on Institute of Electrical and Electronic Engineers (IEEE) 802.11 standards. Among the IEEE 802.11 standards, an IEEE 802.11s standard, in which a cable connection between Access Points (APs) is not required, has been actively developed. A WLAN communication system defined in the IEEE 802.11s standard is referred to as a “WLAN mesh communication system.” The WLAN mesh communication system is mainly installed in an area in which it is difficult to install a general WLAN communication system defined in an IEEE 802.11a standard. Hereinafter, the general structure of a WLAN mesh communication system will be described with reference to FIG. 1.
FIG. 1 is a block diagram illustrating the general structure of the WLAN mesh communication system.
Referring to FIG. 1, the WLAN mesh communication system includes a Mesh AP Portal (MAPP) 111 connected to a wired network 101 by wire, a plurality of MAPs 121, 131, 141 and 151, and Subscriber Stations (SSs) 113, 115, 117, 123, 125, 127, 133, 135, 137, 143, 145, 147, 153, 155 and 157 for receiving a communication service from the MAPP 111 and the MAPs 121, 131, 141 and 151. The MAPP 111 functions as both a Mesh Point (MP) and an AP, and each of the MAPs 121, 131, 141 and 151 functions as both the MP and the AP.
The MAPP 111 performs the same functions as those of the MAPs 121, 131, 141 and 151, and also functions as a gateway of the WLAN mesh communication system by connecting a wireless network to the wired network 101 by wire. The MAPP 111 and the MAPs 121, 131, 141 and 151 form mesh links 161, 163, 165, 167 and 169. The formed mesh links 161, 163, 165, 167 and 169, or the MAPP 111 and the MAPs 121, 131, 141 and 151 all include MPs, so as to function as the MP, respectively. The MAPP 111 and the MAPs 121, 131, 141 and 151 function as the MP. Further, the MAPP 111 and the MAPs 121, 131, 141 and 151, which function as the AP, respectively include a predetermined number of SSs, so that local networks 110, 120, 130, 140 and 150 are formed.
In the meantime, the MAPP 111 and the MAPs 121, 131, 141 and 151 transmit beacon messages to adjacent MAPs or MAPP, and receive beacon messages from the adjacent MAPs or the MAPP. The beacon message includes both location information for reporting their own existence through each of the mesh links 161, 163, 165, 167 and 169 formed between the MAPP 111 and the MAPs 121, 131, 141 and 151, and performance information for reporting their own ability to function as the AP and the MP. Herein, the MAPP 111 and the MAPs 121, 131, 141 and 151 periodically transmit their own beacon messages to the adjacent MAPs or MAPP at regular intervals stipulated in the aforementioned IEEE 802.11s standard.
However, since the WLAN mesh communication system defined in the IEEE 802.11s standard has not stipulated both an interval, in which the MAPP 111 and the MAPs 121, 131, 141 and 151 transmit their own beacon messages, and an interval, in which the MAPP 111 and the MAPs 121, 131, 141 and 151 receive beacon messages from the adjacent MAPs or MAPP, many problems may occur in transmission/reception of the beacon messages of the MAPP 111 and the MAPs 121, 131, 141 and 151. For example, the second MAP 131 may receive beacon messages from the MAPP 111 and the MAPs 121, 141 and 151 while transmitting its own beacon message to the MAPP 111 and the MAPs 121, 141 and 151 between which the mesh links 161, 165, 167 and 169 have been formed. Further, after the second MAP 131 transmit its own beacon message, the second MAP 131 may receive the beacon message of the third MAP 141 from the third MAP 141, between which the mesh link 167 has been formed, while receiving the beacon message of the first MAP 121 from the first MAP 121. Therefore, mutual collision and interference may occur in the beacon messages transmitted/received at the same time as described above, so that the beacon messages may not be normally transmitted/received. Accordingly, the performance of the communication system may deteriorate. That is, since the WLAN mesh communication system defined in the IEEE 802.11s standard has stipulated only the transmission period of a beacon message, and has not considered a detailed scheduling method of a beacon period for the transmission/reception of a beacon message, it is necessary to provide the scheduling method for the transmission/reception of the beacon message.